/*
 * Copyright (c) 2011-2012 Alexander Dubu
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * o  Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * o  Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * o  Neither the name Axil nor the names of its contributors may be used to
 *    endorse or promote products derived from this software without specific
 *    prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
package axil.api.access;

import axil.api.Context;


/**
 * An object for accessing a value from a context. For a simple identifier,
 * this is typically just the lookup of the name in the context via the get()
 * method. For a compound identifier (one composed of multiple elements separated
 * by '.' characters), the accessor should provide an efficient mechanism for
 * navigating the identifier's elements and returning the value. For example,
 * consider this compound identifier:
 * <pre>
 *     `Shopping Cart.Customer.Last Name`
 * </pre>
 * Assuming that only the "Shopping Cart" object is the context, then the
 * "Customer" field from that object must be extracted, and then the "Last Name"
 * field from that object.This interface is intended to be implemented by host
 * applications, as necessary.
 */
public interface Accessor {
	/**
	 * Access the field or object represented by this accessor object.
	 *
	 * @param context
	 * 	The context where the root object of an access path resides. The context
	 * 	given is never null. The context may, or may not, actually contain the
	 * 	desired object.
	 *
	 * @param parent
	 * 	The parent object, if any, from the previous (left hand) element of
	 * 	a compound identifier. For example, in the compound identifier
	 * 	"Shopping Cart.Items", when "Items" is accessed, the parent if the value
	 * 	of "Shopping Cart" extracted from the context. A null value is given
	 * 	when accessing a simple identifier or the root object in a compound
	 * 	identifier.
	 *
	 * @return
	 * 	Returns a null value if the field or object is null. Throws an exception
	 * 	if the field or object simply does not exist.
	 */
	public Object access(Context context, Object parent);
}
